Acrylate functional organosiloxane/oxyalkylene copolymers and electrically conductive compositions containing same and a solubilized lithium salt

ABSTRACT

This invention provides novel liquid organosiloxane/graftoxyalkylene copolymers that cure to yield solid materials wherein at least a portion of the pendant oxyalkylene units are terminated with an acrylate group. The copolymers can be cured by heating them in the presence of suitable curing agents, by exposure to ultraviolet radiation in the presence of a photoinitiator, or by exposure to an electron beam. The copolymers can be combined with solubilized, ionizable lithium salts to yield curable electroconductive compositions suitable for use as electrolytes in storage batteries.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to organosiloxane/oxyalkylene copolymers. Moreparticularly, this invention pertains to polyorganosiloxanes containingpendant oxyalkylene units that are terminated with an acrylate group.The copolymers are curable by ultraviolet or electron beam radiation andare particularly useful as electrolytes in conjunction with solubilized,ionizable lithium salts.

2. Description of the Prior Art

Organosiloxane/oxyalkylene copolymers containing divalent siloxane unitscorresponding to the general formula RGSiO are known in the art. In thisformula R typically represents a monovalent hydrocarbon radical or asubstituted monovalent hydrocarbon radical and G represents a sequenceof at least two oxyalkylene groups such as oxyethylene or oxypropylenethat are bonded to the silicon atom by means of an alkylene radical. Thesequence can be terminated with a hydroxyl group, an alkoxide group or agroup of the formula --O(O)CR', where R' represents a monovalenthydrocarbon radical that is free of ethylenic unsaturation.

U.S. Pat. No. 3,703,489, which issued to Morehouse on Nov. 21, 1972describes silane/oxyalkylene block copolymers wherein from 15 to 60weight percent of the oxyalkylene units are oxyethylene and theremainder are oxypropylene. The sequences of oxyalkylene units areterminated with an alkoxy group containing from 1 to 10 carbon atoms.

The sequence of oxyethylene units in the siloxane/oxyethylene copolymersdisclosed in U.S. Pat. No. 3,560,544, which issued to Haluska on Feb. 2,1971 are bonded to silicon through an alkylene group and are terminatedby groups of the formula --OC(O)R[C(O)OA]_(x), where A represents anamine group, an alkali metal or an alkaline earth metal, R represents adivalent or a trivalent hydrocarbon radical containing from 2 to 6carbon atoms and x is 1 or 2.

U.S. Pat. No. 3,957,843, which issued to Bennett on May 18, 1976,discloses siloxane/oxyalkylene copolymers wherein A of the foregoingformula is hydrogen, a monovalent hydrocarbon radical free of ethylenicunsaturation, --OCNHR', --OCNH2, --OCR', or --OCOR', where R' representsa monovalent hydrocarbon radical that is free of aliphatic unsaturation.

Polyorganosiloxanes containing acrylate functional pendant groups of theformula --R"C--O(O)CCH═CH₂ bonded to at least a portion of the siliconatoms are described in U.S. Pat. No. 3,878,263, which issued to Martinon July 10, 1972. In this instance the acrylate group is bonded tosilicon through a divalent hydrocarbon radical that can optionallycontain an ether linkage. A sequence of oxyalkylene units is notmentioned as a possible candidate for the R" group.

The absence of acrylate or other ethylenically unsaturated terminalgroups on many prior art siloxane/oxyalkylene copolymers isunderstandable, based on the intended use of these copolymers. All ofthe references cited hereinabove that disclose siloxane/oxyalkylenecopolymers teach using these copolymers as surfactants for thepreparation of polyurethane foams. These surfactants are intended tofacilitate foam formation, and typically do not require the presence ofethylenically unsaturated hydrocarbon radicals.

The prior art pertaining to the use of organosiloxane/oxyalklyenecopolymers as surfactants go so far as to specifically exclude thepresence of ethylenically unsaturated carbon-to-carbon bonds, usually toavoid undesired side reactions during preparation of these copolymers.The copolymers are typically prepared by reacting a monoallyl ether ofthe desired oxyalkylene polymer with a polyorganohydrogensiloxanecontaining an average of at least one silicon-bonded hydrogen atom permolecule. The allyl or other ethylenically unsaturated hydrocarbonradical reacts with the silicon-bonded hydrogen atoms, and appear in thefinal product as an alkylene radicals.

Another known use for liquid polydiorganosiloxanes containing pendantpolyoxyalkylene units is as electrolytes in solid state batteriescontaining ionizable lithium compounds. An article by Hall et al.[Polymer Communications, 27 (4), 98-100 (1986)] discloses copolymersprepared by the base catalyzed reaction between apolymethylhydrogensiloxane and ethylene glycol oligomers terminated onone end by a methoxy group and on the other end by a hydroxyl group. Thereaction product could be crosslinked by heating, and the conductivitywas found to be inversely proportional to the degree of crosslinking.

For many applications, including solid state batteries, it is preferredif not a requirement that the electrolyte be a solid material. This canbe achieved by curing the polymeric electrolyte either prior to orfollowing addition of the ionizable lithium salt.

An article by Fish et al. [Makromol. Chem, Rapid Comm. 7, 115-120(1986)] reports conductivity data for reaction products of apolymethylhydrogensiloxane and a methoxy-terminated polyethylene oxide.Lithium perchlorate was added to the copolymer before it was cured byheating in the presence of benzoyl peroxide.

An article by Bouridah et al. [Solid State Ionics, 15 (1985), 233-240]describes electrolytes prepared by adding lithium perchlorate to adimethylsiloxane/grafted ethylene oxide copolymer of the formula Me₃SiO(Me₂ SiO)_(x) (MePEOSiO)_(y) SiCH₃ where Me represents methyl, thevalue of x is about 56, the average value of y is about 16 and PEO is--(CH₂ CH₂ O)₂₂ --. The electrolyte is cured by reacting it with anisocyanate. The problem with this method for crosslinking the polymer isthat urethane groups formed during the crosslinking reaction containnitrogen-bonded active hydrogen atoms that can interfere with theelectrochemical reactions occurring in batteries.

Japanese published application no. 217263/85 discloses the addition oflithium perchlorate to a cured polymer having repeating units of theformula ##STR1## where Me represents methyl and the value for n notspecified but is equivalent to a liquid polymer. The polymer is swollenusing acetone prior to addition of the lithium salt.

Crosslinked polymers are typically undesirable as starting materials forpreparing electrolytes because it is difficult to incorporate largeamounts of ionizable salts into these materials even after the polymersare swollen using organic liquids such as acetone.

An article by Nagaka et al. [J. Poly. Sci., Polymer Letters, 22 (12),659-63, 1984] reports high ionic conductivity for uncured polymershaving repeating units of the formula disclosed in the aforementionedJapanese published application and containing a solubilized lithiumsalt.

The present inventors have found that organosiloxane/oxyethylenecopolymers of the prior art containing solubilized lithium salts areoften difficult to cure using organic peroxides or a hydrosilationreaction between silicon-bonded hydrogen atoms and lower alkenylradicals such as vinyl. One aspect of the present invention resides in aclass of organosiloxane/oxyethylene copolymers that do not have thisdisadvantage.

SUMMARY OF THE INVENTION

An objective of this invention is to provide liquidorganosiloxane/oxyalkylene copolymers that cure in the presence ofsolubilized lithium salts to yield solid materials. These copolymers areparticularly useful as electrolytes in solid state batteries. Thecopolymers can be cured by heating in the presence of organic peroxidesor by exposing them to ultraviolet radiation.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention relates to liquid, curablecompositions comprising a copolymer having the general formula

    R.sup.1.sub.3 SiO(R.sup.2.sub.2 SiO).sub.x (R.sup.3 R.sup.4 SiO).sub.y (R.sup.3 R.sup.5 SiO).sub.z SiR.sup.1.sub.3,              (I)

where R¹, R², and R³ represent monovalent hydrocarbon or substitutedmonovalent hydrocarbon radicals, R⁴ represents --R⁶ O(CH₂ CH₂ O)_(m) A,R⁵ represents --R⁷ O(CH₂ CH₂ O)_(n) C(O)CR⁸ ═CH₂, R⁶ and R⁷ representidentical or different alkylene radicals containing from 2 to 12 carbonatoms, R⁸ represents methyl or hydrogen, A represents an alkyl, aryl, oracyl radical, the values represented by m and n are from 4 to 30, thevalue represented by x is from 0 to 100, the value represented by y isfrom 0 to 100, the value represented by z is at least 2, and the valueof x+y+z is equivalent to a viscosity of up to 1 Pa.s at 25° C.

A second aspect of this invention provides improved electrolytematerials for solid state batteries, where said electrolyte comprises acured organosiloxane/ethylene oxide copolymer and a solubilized,ionizable lithium salt. The improvement comprises (1) the presence assaid copolymer of a liquid copolymer exhibiting the general formula

    R.sup.1.sub.3 SiO(R.sup.2.sub.2 SiO).sub.x (R.sup.3 R.sup.4 SiO).sub.y (R.sup.3 R.sup.5 SiO).sub.z SiR.sup.1.sub.3,              (I)

where R¹ -R⁵, x, y and z are as defined in the preceding specificationand (2) a molar ratio of CH₂ CH₂ O units to lithium salt of from 7 to30.

The copolymers of this invention can be prepared using prior art methodsfor preparing diorganosiloxane/graftethylene oxide copolymers. Typicallya diorganosiloxane/organohydrogensiloxane copolymer corresponding to theformula

    R.sup.1.sub.3 SiO(R.sup.2.sub.2 SiO).sub.x (R.sup.3 HSiO).sub.y+z SiR.sup.1.sub.3                                           (II)

is reacted with at least one of two classes of liquid polyethyleneoxides (also referred to herein as polyethylene glycols) containing oneethylenically unsaturated terminal group. The first class is terminatedon one end with a triorganosiloxy group and corresponds to the formula

    R.sup.7* O(CH.sub.2 CH.sub.2 O).sub.n SiR.sup.9.sub.3      (III)

The second class of polyethylene oxides is optional and corresponds tothe formula

    R.sup.6* O(CH.sub.2 CH.sub.2 O).sub.m A.                   (IV)

R^(6*) and R^(7*) represent terminally unsaturated alkenyl radicalscontaining the same number and configuration of carbon atoms as the R⁶and R⁷ groups, respectively and R⁹ represents a monovalent hydrocarbonor substituted monovalent hydrocarbon radical selected from the samegroup as R¹. R⁹ is most preferably methyl.

Following reaction with the copolymer of formula II the triorganosiloxyterminal groups of the polyethylene oxide units represented by formulaIII are converted to hydroxyl groups by reacting the copolymer with anexcess of an alcohol such as methanol. These hydroxyl groups are thenreacted with an organometallic compound such as an organolithiumcompound followed by reaction with acryloyl chloride or methacryloylchloride to form the corresponding acrylic or methacrylic acid ester.

As a rule the total number of moles of polyethylene oxides correspondingto formulae III and IV is approximately equal to the number of moles ofsilicon bonded hydrogen atoms present in the reaction mixture.

The reaction between the aforementioned organohydrogensiloxanehomopolymer or copolymer and the polyethylene oxide(s) is conducted inthe presence of a platinum-containing catalyst of the type typicallyused for hydrosilation reactions. Halogen-containing platinum compoundssuch as hexachloroplatinic acid and complexes of these compounds withethylenically unsaturated organosilicon compounds are preferredcatalysts.

Because the polyorganosiloxane and the polyethylene oxides representedby formulae III and IV are incompatible it is usually desirable toinclude in the reaction mixture an organic liquid that is a solvent forall reactants and the final copolymer. Preferred solvents include butare not limited to liquid hydrocarbons such toluene and cyclic etherssuch as tetrahydrofuran. To facilitate isolation of the final copolymerthe solvent should be capable of being evaporated from the reactionmixture under reduced pressure at temperatures from about 20° to 30° C.

It is desirable to add small amounts of an anti-oxidant such ashydroquinone to the resultant reaction mixture to prevent prematurecuring of the copolymer by polymerization of the acrylate ormethacrylate groups.

Specific reaction conditions for the preparation of preferred copolymersof this invention are described in the accompanying examples.

The radicals and numerical values represented by R¹, R², R³, R^(6*),R^(7*), R⁸, R⁹, A, m, n, x, y, and z in formulae II, III and IV aredefined in the preceding specification. The terminal group of theoptional polyethylene oxide corresponding to the foregoing formula IV isrepresented by A, where A is defined as an alkyl or aryl radical or anacyl group represented by R¹⁰ C(O)--, where R¹⁰ is an alkyl radical thatpreferably contains no more than 4 carbon atoms. Most preferably R¹⁰represents a methyl or ethyl radical.

In preferred embodiments of the present copolymers R^(6*) and R^(7*) areethylene or propylene and A is preferably an alkyl radical or an acylgroup and contains from 1 to 4 carbon atoms.

The silicon-bonded hydrocarbon and substituted hydrocarbon radicalsrepresented by R¹, R² and R³ preferably contain from one up to about 10carbon atoms that can be arranged in linear or branched configurations.The radicals preferably are lower alkyl, lower haloalkyl or phenyl, thispreference being based on the availability of the starting materialsused to prepare the aforementioneddiorganosiloxane/organohydrogensiloxane copolymer. Preferred radicalsinclude but are not limited to alkyl radicals such as methyl, ethyl andpropyl, haloalkyl radicals such as 3,3,3-trifluoropropyl, cycloalkylradicals such as cyclohexyl, aryl radicals such as phenyl and alkarylradicals such as tolyl.

When the copolymers of this invention are used as electrolytes for solidstate batteries in combination with a solubilized lithium salt theradicals represented by R¹, R² and R³ are preferably methyl.

The values of m, n, x, y, and z in the formula for the presentcopolymers determine the viscosity of the copolymer and the crosslinkdensity of the cured material. The value of x, representing the numberof diorganosiloxane units present in the copolymer, can be from 0 up to100, the value of y can be from 0 to 100, the value for z is at least 2,and the sum of x, y and z is at least 10. When this sum is less than 10and the value of z is less than 2 the copolymer cannot be cured to forma solid material.

Preferably the values represented by x, y and z are from 0 to 35 for x,from 0 to 20 for y, from 4 to 12 for z, and the sum of x, y and z isfrom 10 to 50. Copolymers of this type exhibit a viscosity of less than1 Pa.s at 25° C.

The polyethylene oxides represented by formulae III and IV each containan average of from about 4 to about 20 repeating units per molecule,which represents the values assigned to m and n in the precedingformulae. This value is preferably between 4 and 12.

The electrical conductivity of the present copolymers is determined, atleast in part, by the crosslink density of the copolymer. Crosslinkdensity can be expressed in terms of the molecular weight of thatportion of the copolymer molecule separating the ethylenicallyunsaturated terminal groups of adjacent polyethylene oxide chainsrepresented by R⁵ in the foregoing formula.

For the present copolymers the theoretical value for the molecularweight between crosslinks, referred to hereinafter as MW_(c), iscalculated by dividing the molecular weight of the copolymer by theaverage number of moles of R⁵ units per molecule.

MW_(c) values can be determined experimentally by measuring the carbinolgroup content of a copolymer wherein the C(O)CR⁸ ═CH₂ group of theterminal group represented by R⁵ is replaced by the hydroxyl group ofthe intermediate that is reacted with acryloyl- or methacryloyl chlorideto obtain the R⁵ group.

Experimental data demonstrates that for preferred copolymers usefulconductivity values, typically greater than about 10⁻⁵ (ohm cm.)⁻¹,cannot be achieved at MW_(c) values below about 1000. The conductivityreaches a maximum at an MW_(c) value of about 1500 and remains at thismaximum up to at least an MW_(c) value of 10,000.

Copolymers with an MW_(c) value of above about 3000 may not containsufficient acrylate- or methacrylate terminated polyethylene oxide unitsto provide the crosslink density needed to form a solid cured material.In these instances an external crosslinking or curing agent such as adifunctional or trifunctional ester of acrylic or methacrylic acid mustbe used.

Examples of suitable external curing agents include but are not limitedto ethylene glycol dimethacrylate and trimethylolpropanetrimethacrylate.

The amount of lithium salt that can be dissolved in the copolymer isdirectly related to the total number of ethylene oxide units present ina given weight of copolymer, i.e. the values of m, n, y and z.Solubilization of one mole of the lithium salt requires from 7 to 30moles of ethylene oxide (--CH₂ CH₂ O--) units in the copolymer. Above aratio of 30 moles of ethylene oxide units per mole of salt theconductivity of the copolymer decreases below a useful value.

The presence of the acryloxy or methacryloxy group allows curing of thecopolymer to be initiated either by free radicals generated by thedecomposition of organic peroxides or by irradiation with ultravioletlight or an electron beam. The use of curing reactions involving activehydrogen atoms can interfere with electrochemical reactions.

A preferred method for curing mixtures of thediorganosiloxane/graft-polyethylene oxide copolymers of this inventionand a solubilized lithium salt is by exposing films or coatings formedfrom these mixtures to ultraviolet radiation in the presence of aphotoinitiator. Suitable photoinitiators include but are not limited toaromatic ketones such as benzophenone, alkoxy substituted acetophenonessuch as diethoxyacetophenone and dimethoxyphenylacetophenone, benzil,and cationic initiators such as triaryl sulfonium-, diazonium- andphosphonium salts.

The exposure time and wavelength of the radiation required to cure thecopolymer is dependent upon the type and concentration ofphotoinitiator, the thickness of the layer to be cured and the intensityof the ultraviolet radiation at the surface of the copolymer. Coatingsand self-supporting films measuring up to about 2 mm. in thickness andformed from preferred lithium-containing copolymers of this inventionare completely cured following exposures of one second or less toultraviolet radiation. The films and coatings are cured by passing themunder an ultraviolet lamp at speeds of from about 50 to about 100 feetper minute. The radiation dosage at the surface of the film or coatingis preferably equivalent to from 50 to 200 millijoules per square cm.

The present copolymers containing solubilized lithium salts can also becured by irradiating them with an electron beam or by heating in thepresence of an organic peroxide or an azo compound. Suitable peroxidesinclude benzoyl peroxide, bis(2,4-dichlorobenzoyl) peroxide and dicumylperoxide. Suitable azo compounds include azo bis-isobutyronitrile. Itwill be understood that the temperature used to cure the copolymer mustbe above the decomposition temperature of the organic peroxide or azocompound. The peroxides are typically used at a concentration of from0.2 to about 2 weight percent, based on the weight of the copolymer.

As disclosed hereinabove the present copolymers are particularly usefulas electrolytes for solid state batteries. In this application fromabout 0.033 to about 0.14 mole of an ionizable lithium salt per mole ofethylene oxide (--CH₂ CH₂ O--) units in the copolymer is dissolved inthe copolymer prior to curing. This concentration of salt is typicallysufficient to achieve conductivity values of from 1×10⁻⁶ to about 3×10⁻⁵for the cured copolymer/salt composite.

Data in the accompanying examples demonstrate that a major factoraffecting conductivity is the composition of the copolymer, particularlythe crosslink density of the copolymer and the total concentration ofethylene oxide units. The composition of the copolymer will determinethe molecular weight between crosslinks, referred to hereinbefore asMW_(c).

It has been found that the concentration of lithium salt has some effecton the conductivity of a particular copolymer. Data in the accompanyingexamples demonstrate that for a particular copolymer the conductivityincreases by a factor of about 2 in conductivity as the ratio of thenumber of moles of lithium salt to ethylene oxide units is increasedfrom 0.05 to 0.08.

To facilitate solubilization of the salt it is preferably added to thecopolymer as a solution in a non-aqueous liquid medium such astetrahydrofuran.

Suitable lithium compounds include salts of acids having pK_(a) valueslower than about 3 and which are soluble in the presentorganosiloxane/ethylene oxide copolymers, Examples of suitable saltsinclude but are not limited to organosulfonic acids, phosphoric acid andperchloric acid.

An advantage of the present copolymers is that curing of the copolymeris not inhibited to any significant extent by the presence of theionizable lithium salt.

The following examples describe the preparation of preferred copolymersof this invention and their use in combination with solubilized,ionizable lithium salts as electrolytes in solid state batteries. Unlessotherwise indicated all parts and percentages are by weight andviscosities were measured at 25° C. The term polyethylene glycol used inthe examples is synonymous with the term "polyethylene oxide" describedin the preceding specification.

EXAMPLE 1

Preparation of Me₃ SiO(MeXSiO)₃₈ (MeYSiO)₁₂ SiMe₃ ; Me is methyl, X isCH₂ CH₂ CH₂ (OCH₂ CH₂)₁₂ O(O)CCH₃, and Y is CH₂ CH₂ CH₂ (OCH₂ CH₂)₁₂O(O)CCH═CH₂.

This example describes the preparation of a preferred copolymer of thisinvention. The terms "polyethylene glycol" and "polyethylene oxide" areused interchangeably.

A glass reactor equipped with a stirrer, water-cooled condenser and anitrogen inlet was charged with 56.1 parts of atrimethylsiloxy-terminated polymethylhydrogensiloxane containing about1.6 weight percent of silicon-bonded hydrogen, 580 parts of the allylether of a polyethylene glycol monoacetate exhibiting a degree ofpolymerization of 12, 42 parts of the trimethylsiloxy-terminatedmonoallyl ether of a polyethylene glycol exhibiting a degree ofpolymerization of 12, and 261 parts of dry toluene. Thetrimethylsiloxy-terminated polyethylene glycol was prepared by reactingthe corresponding monoallyl ether with 1.5 moles of hexamethyldisilazaneper mole of carbinol groups. The mixture was heated to a temperaturejust below the boiling point of the solvent.

The addition of 0.5 part of a 10 weight percent hexachloroplatinic acidsolution in isopropanol to the solubilized mixture of the twopolyethylene glycols and the organohydrogensiloxane resulted in anexothermic reaction that generated sufficient heat to raise thetemperature of reaction mixture to the boiling point for severalminutes. Following this period the reaction mixture was then heated tomaintain it at the boiling point for two hours. The reaction mixture wasthen cooled to about 60° C., at which time 80 parts of methanol wereadded and heating was continued for an additional two hours. A portionof contents of the reactor were then distilled under ambient pressureuntil the temperature of the liquid in the reactor reached 140° C. Thedistillate was discarded. Any residual solvent or methanol was removedby heating the reaction mixture under a pressure of 5 torr until thetemperature of the liquid reached 150° C.

A turbid liquid exhibiting a hydroxyl number of 7221.1 was obtained in93 percent yield. 100 grams of this liquid and 25 cc tetrahydrofuranwere charged into a glass reactor equipped with a stirrer, water cooledcondenser and a nitrogen inlet. 14.4 cc of a 1.6M solution of n-butyllithium in hexane was then added to the reaction mixture through asyringe. A small amount of solid formed and the viscosity of thereaction mixture increased following the addition. 75 cc oftetrahydrofuran were then added, followed by 2.93 cc of acryloylchloride by means of a syringe. After stirring at room temperature for15 minutes 0.05 g of hydroquinone was added to stabilize the reactionproduct, following which the reaction mixture was concentrated underreduced pressure using a water bath at a temperature of 40°-50° C. toprevent freezing of the resultant copolymer of this invention.

A ten gram sample of the copolymer was blended with 5.42 g. of a 33.2weight percent solution of lithium trifluoromethylsulfonate intetrahydrofuran, equivalent to a polyethylene glycol/lithium molar ratioof 18. This mixture was then blended with 0.1 g ofazo-bis-isobutyronitrile as a free radical initiator and molded for 30minutes at a temperature of 85°-90° C. to yield a 1 mm-thick film ofcured, bubble-free conductive elastomer.

The electrical conductance of the molded film was measured in anenclosed shielded chamber under a nitrogen atmosphere at ambienttemperature. The measuring apparatus consisted of a lower squarestainless steel electrode having an edge dimension of 2.5 cm and anupper electrode in the form of a vertically oriented stainless steel rodhaving a circular cross-section measuring 0.315 cm² in area. The samplewas placed between the two electrodes and in contact with the surface ofeach electrode.

The equipment used to measure the conductivity of the sample consistedof a Wavetek model 186 frequency generator set to provide an output of 1volt_(eff) at frequencies of from 1 Hz to 100 kHz., a data acquisitionand control box (model 3497A manufactured by Hewlett PackardCorporation), an IIEE 488 bus that connected the dataacquisition/control box to a Hewlett Packard model 9920 series 200computer and a model SR510 lock-in amplifier manufactured by SanfordResearch Systems. The output of the frequency generator was connected tothe lower electrode. The upper electrode was connected to the lock-inamplifier through a 1 ohm resistor. The lock-in amplifier also sampledthe output of the frequency generator.

Considering the two electrodes as plates of a capacitor and the testsample as the dielectric, the conductivity of the sample was determinedby applying the output of the frequency generator to the lowerelectrode. The current through the 1 ohm resistor and the phase anglebetween the voltage and the current were determined using the lock-inamplifier. This procedure was repeated at a number of differentfrequencies between 1 Hz and 100 kHz to provide a plot of the realcomponent of the total impedance as the abscissa and the imaginarycomponent as the ordinate as a function of frequency. Extending the plotto the point at which it intersected the abscissa at the point furthestfrom the ordinate yielded the purely resistive component (R) of theimpedance. The resistivity (p) was then calculated from the geometry ofthe upper electrode using the formula p=RA/d, where A is the area of theupper electrode (0.315 cm²) and d is the thickness of the sample, 0.1cm. The conductivity of a sample is the reciprocal of its resistivity.

The conductivity value for sample 2 was 1.6×10⁻⁵ (ohm-cm.)⁻¹.

EXAMPLE 2

This example demonstrates the effect of the molecular weight betweencrosslinks, referred to hereinbefore as MW_(c), on the conductivity ofvarious dimethylsiloxane/ethylene oxide copolymers. Ten copolymers ofthis invention were prepared and cured using the procedure described inExample 1. An additional two copolymers having MW_(c) values below thescope of the present invention were prepared for purposes of comparison.

The trimethylsiloxy-terminated methylhydrogensiloxane homopolymer anddimethylsiloxane/methylhydrogensiloxane copolymers used as intermediateswere prepared using known methods and are represented by the averageformula Me₃ SiO(Me₂ SiO)_(x) (MeHSiO)_(y+z) SiMe₃.

The two types of allyl ether-terminated polyethylene oxides arerepresented by the general formulae CH₂ ═CHCH₂ O(CH₂ CH₂ O)_(m) SiMe₃and CH₂ ═CHCH₂ O(CH₂ CH₂ O)_(m) C(O)CH₃. The trimethylsiloxy-terminatedpolymer was used alone or in combination with a polyethylene oxidecontaining the same number of repeating units and an acetoxy terminalgroup. The molar ratio of the acetoxy-terminated polyethylene oxide tothe trimethylsiloxy-terminated polyethylene oxide is represented by y/zin the following listing of reactants. The trimethylsiloxy group wasconverted to the acryloxy group using the procedure described in Example1.

The siloxane polymers and the allyl ether-terminated polyethylene oxidesused to prepare the samples evaluated in this example are identified aslisted in Tables 1 and 2, the terms x, y, and z referring to theforegoing formulae.

The conductivity values for the ten samples of this invention and 3controls, together with the molecular weight between crosslink sites(MW_(c)) are listed in Table 3.

                  TABLE 1                                                         ______________________________________                                        ORGANOHYDROGENSILOXANES                                                       Reactant                                                                      Designation      x      y + z                                                 ______________________________________                                        A                33.3   16.7                                                  B                0      50                                                    C                7.7    3.3                                                   D                0      10                                                    E                5      5                                                     F                0      30                                                    G                25     25                                                    H                20     10                                                    I                15     15                                                    ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        POLYETHYLENE OXIDES                                                           Reactant Designation                                                                     m                                                                  ______________________________________                                                 K   4                                                                         L   8                                                                         M   12                                                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Copolymer Composition                                                                   Polyethylene Oxide(s)                                               Siloxane           --OSiMe.sub.3                                                                           --OC(O)CH.sub.3                                  No.  Type   Grams   Type (g)     (g)      y/z                                 ______________________________________                                        1    A      100     L    45      207      0.44/0.10                           2    B      100     L    56.8    449.6    1.88/0.12                           3    C      100     L    198     0          0/0.42                            4    D       25     L    61.5    144      0.30/0.13                           5    E      100     M    66.7    431.6    0.72/0.10                           6    K      100     M    303     178.2    0.30/0.45                           7    H      100     M    107.5   221      0.37/0.16                           8    F       50     M    62.6    497      0.83/0.09                           9    I       20     K    12.1    114      0.33/0.03                           10   J      100     M    77      307.9    0.65/0.16                           1C*  E      31.2    K    11.2    77.8     0.22/0.03                           2C*  E      32.9    K    53.7    33.8      0.1/0.15                           3C*  H       42     K    24.3    53.7     0.15/0.07                           ______________________________________                                          *Control Example                                                        

                  TABLE 4                                                         ______________________________________                                                           Conductivity                                               No.         MW.sub.c                                                                             × 10.sup.5 (ohm cm).sup.-1                           ______________________________________                                        1           3400   1.5                                                        2           4500   1.3                                                        3           1090   0.72                                                       4           1040   0.32                                                       5           6020   2.1                                                        6           1290   0.42                                                       7           2920   3.2                                                        8           4760   2.3                                                        9           1230   4.0                                                        10          1670   2.4                                                        1C           930   0.092                                                      2C           540   0.0092                                                     3C           940   0.003                                                      ______________________________________                                    

EXAMPLE 3

This example demonstrates the ability of the present copolymers to cureby exposure to ultra-violet radiation. A ten gram portion of thecopolymer of this invention described in Example 1 was blended with 5.4g. of a 33.3 weight percent solution of lithiumtrifluoromethanesulfonate in tetrahydrofuran. The tetrahydrofuran wasremoved under reduced pressure and 0.2 g. of2-hydroxy-2-methyl-1-phenylpropan-1-one was added. The resultant liquidwas coated as an approximately 0.1 mm-thick layer on an aluminum panel.The coated panel was then exposed to an amount of radiation from amedium pressure ultraviolet lamp equivalent to 36.5 millijoules/cm². Thepanel was passed twice under the lamp on a belt traveling at a speed of55 feet (16.8 meters) per minute. The belt was located 15 cm. below thelamp. The resultant cured coating was non-tacky and elastomeric.

EXAMPLE 4

This example demonstrates the effect of the molar ratio of lithium saltto ethylene oxide units on the conductivity of the cured elastomer. Foursamples were prepared using the copolymer described in Example 1 andvarious amounts of lithium trifluoromethanesulfonate as a 33 percentsolution in tetrahydrofuran. The amounts of lithium salt added wereequivalent to a molar ratio of ethylene oxide (EO) to lithium salt (Li)of 12, 15, 18 and 21. Samples of each of these copolymers were preparedfor conductivity measurements as described in the preceding Example 2.Conductivity measurements were conducted on these samples as describedin Example 2 with the following results.

    ______________________________________                                        EO/Li      Conductivity [× 10.sup.-5 (ohm cm).sup.-1 ]                  ______________________________________                                        12         1                                                                  15         1.4                                                                18         1.6                                                                21         1.8                                                                ______________________________________                                    

EXAMPLE 5

This example demonstrates that compositions of this invention can becured using an electron beam. A curable, electroconductive compositionwas prepared using the ingredients specified for sample 6 in table 3 ofexample 2. Test samples were prepared as described in example 1, withthe exception that the azo-bis-isobutyronitrile was not added and thesample was cured by exposing it to an electron beam produced by a ModelEB-150 generator manufactured by Energy Sciences. The total dosage wasbetween 3 and 4 megarads.

That which is claimed is:
 1. A liquid, curable copolymer having thegeneral formula R¹ ₃ SiO(R² ₂ SiO)_(x) (R³ R⁴ SiO)_(y) (R³ R⁵ SiO)_(z)SiR¹ ₃, where R¹, R², and R³ represent monovalent hydrocarbon orsubstituted monovalent hydrocarbon radicals, R⁴ represents --R⁶ O(CH₂CH₂ O)_(m) A, R⁵ represents --R⁷ O(CH₂ CH₂ O)_(n) C(O)CR⁸ ═CH₂, R⁶ andR⁷ represent identical or different alkylene radicals containing from 2to 12 carbon atoms, R⁸ represents methyl or hydrogen, A represents analkyl, aryl, or acyl radical, the values represented by m and n are eachfrom 4 to 30, the values represented by x and y are each from 0 to 100,the value represented by z is at least 2, and the value of x+y+z isequivalent to a viscosity of up to 1 Pa.s at 25° C.
 2. A compositionaccording to claim 1 where R¹, R² and R³ are methyl, phenyl or3,3,3-trifluoropropyl, R⁶ and R⁷ are ethylene or propylene, A representsan alkyl or acyl radical and contains from 1 to 4 carbon atoms, m and nare from 4 to 12, inclusive, x is from 0 to 35, inclusive, y is from 0to 20, z is from 4 to 12 and the total of x, y and z is from 10 to 50.3. A composition according to claim 2 where R¹, R² and R³ are methyl, R⁸is hydrogen and A is acetyl.